1. Field of the Invention
The present invention relates to an organic light emitting device (OLED) in which a fused compound or its derivatives are used as the emissive layer and/orone or more of the charge transport layers, or as a host material in an OLED.
2. Description of the Related Art
Electroluminescence materials are materials which are capable of radiating light on application of an electric field. The physical model for describing this effect is based on the radiative recombination of electrons and electron gaps (holes). In light-emitting diodes, the charge carriers are injected via the cathode or anode into the electroluminescence material. Electroluminescence devices comprise a luminescence material as a light-emitting layer.
Significant efforts have been expended in developing suitable electroluminescence materials for use in organic light emitting devices (OLEDs). Such devices are commercially attractive because they offer the promise of low-cost fabrication of high-density pixeled displays exhibiting bright electroluminescence with long life times and wide color range.
A simple OLED is fabricated by sandwiching an emissive layer between an anode and a cathode. When a bias is applied across the electrodes, holes and electrons are respectively injected from the anode and cathode into the emissive layer, typically facilitated by hole transport and electron transport layers adjacent to the respective electrodes. The holes and electrons radiatively combine in the emissive layer and emit light. Improved performance can be obtained if blocking layers are provided to block against the injection of either holes or electrons from the adjoining layer and their subsequent escape from the device. As further examples, a double-layered structure is fabricated from a combined hole-injecting and transporting layer together with a combined electron-transporting and light-emitting layer. Likewise, a triple-layered structure is compose of a hole-injecting and transporting layer, a light-emitting layer, and an electron-injecting and transporting layer.
In addition, it is possible to form these layers from a host material doped with another material designed to achieve the desired effect of the layer (for example, to achieve a hole transport effect, an electron transport effect, or an emissive effect).
Some of these layers can be combined, such as devices which obtain electroluminescence through doping of an electron transport layer with flourescent dye materials.
Because of consumer expectations of good efficiency, long lifetime and pure color for OLEDs, a need exists for development of suitable materials for the various layers. The desired material used for OLED should ideally combine the following properties: 1) Suitable conjugation to meet band gap requirements for optimal charge injection and color requirements; 2) Easy processability for thin film formation with good morphology; 3) High thermal stability; 4) Long-term stability during device operation and in storage.
Conjugated polymer semi-conductors have attracted attention for optoelectronic applications that traditionally have been the domains of inorganic semi-conductors. The structural flexibility, the very low cost for processing, and the flexible thin film features of conjugated polymers make organic semi-conductive polymer devices competitive with the inorganic semi-conductors. Most conjugated polymers are highly luminescent, and they have attracted great attention in light-emitting device applications.
Many fused aromatic compounds can basically meet the above requirements, but they have low solubility and are difficult to prepare and purify. One way to solve the solubility problem is the use of a spiro configuration.
Spiro compounds are compounds in which two ring systems are linked via a single tetravalent atom. The tetravalent atom is referred to as the spiro atom. Handbook of Chemistry and Physics, 62d Edition (1981-2), CRC Press, pages C-23-C-25. The basic structure of the spiro atom compound can be generally illustrated by 1, below. 
A typical example of a spiro compound is shown below as compound 2. 
Most spiro compounds are very soluble even with a long conjugated aromatic ring system.
Spiro compounds are known to be luminescent and their use in light emitting devices has been suggested.
For example, U.S. Pat. No. 5,621,131 suggests polymers of a monomer having a spiro structure as an electroluminescent material.
U.S. Pat. No. 5,026,894 relates to a spiro compound with a defined physical structure for use in forming semiconducting polymers with perpendicularly arranged cores. The compounds with perpendicularly arranged cores could then be used in memory, logic and amplification computing systems.
U.S. Pat. No. 5,763,636 asserts that certain conjugated polymers having a plurality of spiro atoms are particularly suitable as electro-luminescence materials. These polymers are highly complex, with many possible substituents.
Conjugated polymers comprising at least one unit based on a heterospiro framework have been alleged to have good properties including good electroluminescence, photoluminescence and high color purity. U.S. Pat. Nos. 5,859,211; 6,329,082.
Polymers of substituted and unsubstituted 9,9xe2x80x2-spirobisfluorenes are recommended for use in light-emitting diodes or electrodes in display applications. Such compounds are said to be blue-fluorescing polymers which are soluble in many solvents and therefore readily applied by conventional coating processes. U.S. Pat. No. 6,132,641. Similar polymeric compounds are also described in U.S. Pat. No. 5,840,217.
Spiro compounds have thus been recommended for use in electronic displays as indicated above. Those prior art compounds have the characteristics of high luminescence, good solubility and excellent color purity due to the prevention of intermolecular aggregation. Such compounds can be actually regarded as the combination of two chromophores being crossed-over each other. However, the non-conjugated spiro atom can also break up the long conjugation and lead to an inferior charge injection property. Further, the good solubility can lead to deterioration over time due to changes in morphology during normal operating conditions or during conditions of elevated temperatures.
This invention relates to electroluminescence materials suitable for use in light-emitting devices and flat-panel displays, and methods of using the same material. Particularly, this invention is aimed to improve the charge injection property of spiro-atom linked luminescent materials.
This invention relates to electroluminescence materials suitable for use in light-emitting devices and flat-panel displays, and methods of using the same material. Particularly, this invention is aimed to improve the charge injection property of spiro-atom linked luminescent materials.
To enhance the charge injection ability while maintaining the non-planar configuration of a spiro compound, it has now been found that an excellent approach is to use a conjugated double bond to bond the two ring system, to form fused aromatic compound as illustrated in 3: 
The above compound 3 does not have a spiro atom as defined above, but rather a vinyl-linking two ring system in a non-planar geometry. This type of compound is a fused compound and can be regarded as a quasi-spiro compound. It has excellent hole transport properties as well as good emissive characteristics. However, its good solubility has a drawback if it is used for a hole transport layer followed with a solution thin film deposition method, such as ink-jet printing and spin-coating technique as the following solution process may damage the hole transport layer. However, this shortcoming can be overcome by cross-linking the fused compounds before or after they have been applied to the desired substrate.
In a further aspect, the present invention is an organic light emitting device, an organic solid state laser, and a method for producing such devices, comprising a transparent electrode; a cathode; and an active layer containing a luminescent polymer according to the present invention.
In a still further aspect, the present invention is a photovoltaic cell, and a method for producing such a cell, comprising an active layer containing a luminescent polymer according to the present invention.
In another aspect, the present invention is an electrochromic display, and a method for producing such a display, comprising an active layer containing a luminescent polymer according to the present invention.
This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiment thereof in connection with the attached drawings.